Specific language impairment (SLI) and autism spectrum disorders (ASD) are complex, highly heritable disorders that involve primary impairments in language and communication. Both disorders are heterogeneous, longer-term outcomes vary considerably, and in families that have a diagnosed child, other relatives may share some behavioral features without meeting diagnostic criteria. At around 12 months, delays in major language and communication milestones are first reported for children later diagnosed with SLI or ASD, but thus far, relatively little is known about signs that may be detected during the first year of life. This research program is designed to address this important clinical and theoretical issue by investigating the early development of infants at risk for these disorders (with risk defined on the basis of an older sibling with a confirmed diagnosis). Building on earlier work by others and our own preliminary data, we propose that neurobehavioral markers of risk in fundamental processing systems (e.g., auditory/speech; visual/social) can be detected in the latter half of the first year of life. This is a highly significant stage because during this time development of both language and social perception depend on critical socially-embedded learning experiences. We hypothesize that infants at risk for SLI and ASD have risk markers that signal problems in speech/communication processing mechanisms; infants at risk for ASD have additional (non-shared) risk markers that signal problems in development that are grounded in socially-embedded experiences. These markers may result in altered developmental trajectories. The specific aims of the research are (1) to identify markers that distinguish between infants at risk for SLI or ASD and low risk controls; (2) to identify the predictors of later SLI and ASD diagnoses (at 36 months of age) from measures collected between 6 and 12 months of age; and (3) to compare developmental trajectories of key language and related social/cognitive measures between 6 and 36 months in infants with and without clinical outcomes. These aims will be pursued in a longitudinal prospective design following infants from 6 to 36 months of age. Data will be collected on language and social perception using behavioral, eye-tracking and neurophysiological measures as well as general measures of cognitive and brain development (head circumference; EEG). The findings from this research will have a significant impact on developing novel clinically useful methods for identifying infants at high risk for SLI and ASD; in turn this will improve their prognosis because it will open the doors for early entry into interventions that are known to lead to better outcomes.